Abstract

In the past decade, episodes of severe air pollution, known as the "black cloud," have occurred in Cairo, Egypt, in the early autumn. In this study, data from the Moderate Resolution Imaging Spectrometer (MODIS) and the Multi-angle Imaging Spectroradiometer (MISR) are used with meteorological data and trajectory analyses to determine the cause of these events. MODIS fire counts put the source as the burning of agricultural waste after harvest season in the Nile delta region. Synchronous MISR data show that these fires create low altitude (< 500 m) plumes of smoke and aerosols which flow over Cairo in a few hours, as confirmed by Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) forward trajectory analyses. Much of the burning occurs at night, when an inversion constrains the plumes to remain in the boundary layer (BL). Convection during the day raises the BL, dispersing these smoke particles until the next night.